In order to save material and respond to the call of the national energy saving, the beverage industry has launched “lightweight packaging”, utilizing lightweight bottles to package carbonated soft drinks and purified water and other drinking water, as the lightweight bottle shown in FIG. 1. It includes the bottle body 100 and the cap 200 connected together with screw thread. Cap 200 is provided with a downward seal ring 210, whose outer diameter on the upper part is slightly larger than the inner diameter of the bottle mouth 110. With its lower end tilting inward, after capping, seal ring 210 will insert inside the bottle mouth 110, and sealing of the lightweight bottle will be achieved with the outer surface of sealing ring 210 and the inner wall of the bottle mouth 110 against each other. Therefore, no gap (for example, that due to abrasions of the bottle inner wall) is allowed at the location where the outer surface of sealing ring 210 and the inner wall of the bottle mouth 110 against each other, or the seal of the lightweight bottle will be harmed, resulting in leakage and scrapped product.
In order to achieve mass production, BFC combi-block has been used to practice lightweight packaging for drinking water in the market, i.e. BFC combi-block can in turn finish processes of blow molding, filling and capping. Before blow molding, the bottle preform shall be heated, for which the preform clamping head on the lower end of the heating chain is inserted into the bottle mouth 110 and the bottle is clamped with it quickly, and the bottle preform driven by the heating chain is rotated through the heating zone, heated by a heating device and then passed to blow molding zone for blow molding. In order to ensure uniform wall thickness resulted, the preform shall be heated evenly. In order to ensure a good seal of the lightweight bottle, the preform clamping head shall not bring any damage to the bottle mouth when it is inserted into the bottle mouth 110 quickly, otherwise it will harm the seal of the packaging of the lightweight bottle.
FIG. 2 shows the preform clamping head made by existing technology, which includes the heating head 12 attached to the lower end of the insert head 11, both of which are connected to the sleeve shaft 14 by the screw 13. Multiple circularly-arranged mounting grooves 15 are provided between the insert head 11 and the heating head 12. In the mounting groove 15, there equipped with stainless steel expanding plate 16, which can slip along the radial direction of heating head 12 in the mounting groove 15. At the location on the outer wall of heating head 12 corresponding to the stainless steel expanding plate 16 is provided rubber ring 17, with which the stainless steel expanding plate 16 contacts heating head 12 elastically. During operating, the preform clamping head carried by heating chain 10 which is driven by power unit goes downward. When stainless steel expanding plate 16 contacts the mouth of the bottle preform, the stainless steel expanding plate 16 under force will slide inward and squeeze the rubber ring 17 to allow the preform clamping head to go down further. When the preform clamping head reaches the preset position, the heating chain 10 will stop going down, the stainless steel expanding plate 16 will stick tightly to the mouth of the bottle preform due to the elasticity of the rubber ring 17, so that the heating chain 10 will transport the bottle preform to the heating zone in rotating way. Since the upper surface of the bottle mouth contacts the lower surface of discharging ring 18, the bottle preform may be released by pulling the sleeve shaft 14 upwards when heating is completed.
However, there are some shortcomings in the preform clamping head under the existing technology: 1. The preform clamping head is assembled from multiple parts, which have to be processed separately, leading to cumbersome processing operations and high cost; 2. The matching accuracy of parts processed separately is difficult to control. The stainless steel expanding plate 16 after assembling is hard to be uniformly distributed around the axis of rotation of the heating chain 10, resulting in deviation of axis of the bottle preform stuck outside the stainless steel expanding plate 16 from the rotation axis of heating chain 10, leading to uneven heating of the bottle preform due to the shaking and thereby harming the quality of blow molding; 3. When assembling the preform clamping head to the sleeve shaft 14, it is necessary to join the insert head 11 to the heating head 12 and attach all stainless steel expanding plate 16 to it firstly and it is quite troublesome indeed; and 4. Since the hardness of the stainless steel expanding plate 16 is much larger than that of the bottle preform made of PET, the stainless steel expanding plate 16 is apt to abrade the bottle inner wall when the preform clamping head is inserted quickly into the bottle mouth, harming the seal of packaging of the lightweight bottle. And the abrasion will be exacerbated with the temperature rise of the stainless steel expanding plate 16.